The invention concerns an air duct, preferably with a cylindrical jacket.
A known air duct of this genus (German Patent 3 429 710) has several axially separated annular diaphragms that fit tightly into the jacket. The inside diameters of the diaphragms are progressively shorter the nearer they are to the base. Since the position of these diaphragms inside the jacket and the size of their aperture can be varied during the operation, the air duct can be adapted to various applications (heating or cooling). Even though this air duct has been proven in practice, it encounters problems when the temperature of the area being heated must differ extensively from that of the incoming air to rapidly heat up industrial areas that have cooled off overnight or over the weekend. In such a situation the uppermost annular diaphragm and the base, which is closed off, will divert the incoming air, which can accordingly flow out only at a downward slope. Thus, when the difference between the temperatures is extensive, the warm air cannot reach the areas where the personnel are located or to the floor.